Small joint manipulation[grabbing 1 or 2 fingers, or 1 or 2 toes] is illegal because it's a lot easier to break/dislocate a person's fingers/toes simply by quickly tugging on them because there's nearly no resistance than if you would get with 3 or more fingers/toes.

Yes, the open palm to the face would still be used, but only by those that don't like their fingers. So no, it's highly doubtful fighters would put palms with fingers spread in the faces of their opponents if small joint manipulation was legal.